IgG2 Antibodies against a Clinical Grade Plasmodium falciparum CSP Vaccine Antigen Associate with Protection against Transgenic Sporozoite Challenge in Mice

Robert Schwenk,Michael Porter,Jennifer Nikki,Andrea Crisanti,Lisa Rein,Sheetij Dutta,Christian F Ockenhouse,Paul D Wightman,Margot Debot,Roberta Spaccapelo

doi:10.1371/journal.pone.0111020

Abstract

The availability of a highly purified and well characterized circumsporozoite protein (CSP) is essential to improve upon the partial success of recombinant CSP-based malaria vaccine candidates. Soluble, near full-length, Plasmodium falciparum CSP vaccine antigen (CS/D) was produced in E. coli under bio-production conditions that comply with current Good Manufacturing Practices (cGMP). A mouse immunogenicity study was conducted using a stable oil-in-water emulsion (SE) of CS/D in combination with the Toll-Like Receptor 4 (TLR4) agonist Glucopyranosyl Lipid A (GLA/SE), or one of two TLR7/8 agonists: R848 (un-conjugated) or 3M-051 (covalently conjugated). Compared to Alum and SE, GLA/SE induced higher CS/D specific antibody response in Balb/c mice. Subclass analysis showed higher IgG2:IgG1 ratio of GLA/SE induced antibodies as compared to Alum and SE. TLR synergy was not observed when soluble R848 was mixed with GLA/SE. Antibody response of 3M051 formulations in Balb/c was similar to GLA/SE, except for the higher IgG2:IgG1 ratio and a trend towards higher T cell responses in 3M051 containing groups. However, no synergistic enhancement of antibody and T cell response was evident when 3M051 conjugate was mixed with GLA/SE. In C57Bl/6 mice, CS/D adjuvanted with 3M051/SE or GLA/SE induced higher CSP repeat specific titers compared to SE. While, 3M051 induced antibodies had high IgG2c:IgG1 ratio, GLA/SE promoted high levels of both IgG1 and IgG2c. GLA/SE also induced more potent T-cell responses compared to SE in two independent C57/BL6 vaccination studies, suggesting a balanced and productive TH1/TH2 response. GLA and 3M-051 similarly enhanced the protective efficacy of CS/D against challenge with a transgenic P. berghei parasite and most importantly, high levels of cytophilic IgG2 antibodies were associated with protection in this model. Our data indicated that the cGMP-grade, soluble CS/D antigen combined with the TLR4-containing adjuvant GLA/SE warrants further evaluation for protective responses in humans.

Highlights

Malaria is a tropical disease that continues to cause wide spread mortality and morbidity in some of the poorest regions in the world
P. falciparum 3D7 strain circumsporozoite protein (CSP) is composed of the N-terminal region which harbors one cysteine residue, followed by 4 NVDP and 38 NANP repeats and a C terminal region that harbors four additional cysteines that form two disulphide bonds (Fig. 2A) [37]
In a mouse immunogenicity study, the CS/C protein produced very low level NANP-specific antibodies and failed to induce protection against transgenic P. berghei challenge [33] and the process development efforts were focused on the CS/D construct

Summary

Introduction

Malaria is a tropical disease that continues to cause wide spread mortality and morbidity in some of the poorest regions in the world. Studies with an alum-adjuvanted RTS,S formulation showed only limited protection in humans. This could be due to the fact that alum induces primarily a TH2-type immune response [2,3] and malaria infection is known to be at least partially controlled by cellular immunity [4]. Vaccination with RTS,S+AS series adjuvants has since been shown to reproducibly protect ,30–50% of vaccine recipients [5,6] and protection has been associated with the induction of high levels of CSP-specific antibodies and cytokine producing (IL-2+ and IFN-c+) CD4+ T cells [6,7]

Methods

Results

Conclusion